A dinosaur fossil discovered in rural Old Snowmass turned out to be a very rare beast indeed, according to the paleontologist leading the excavation.

The bones are from a haplocanthosaurus, a plant-eater that roamed the earth in the Late Jurassic period, more than 150 million years ago, according to John Foster, curator of paleontology at the Museum of Western Colorado in Grand Junction.

“It’s a pretty rare beast,” he said.

There are only about 10 haplocanthosaurus known total, Foster said, so it is one of the most rare sauropod dinosaurs in the lower Morrison Formation, a unit of rock that is prolific with dinosaur fossils.

Among the identifiable sauropod specimens from the Morrison, about 27 percent are the famed brontosaurus, the lumbering giant with the tree-trunk legs and ridiculously long neck that kids learn about in grade school. In contrast, the haplocanthosaurus accounts for only 2 percent of the dinosaurs identified from the Morrison, Foster said.

The first one was discovered near Canon City in the late 1800s, and the dinosaur was named in 1903, according to Foster’s research. They have been discovered only near Vernal, Utah, and in Colorado and Wyoming, he said.

Working with the haplocanthosaurus is one of his top professional moments.

“Top three, yeah, definitely,” Foster said.

The bones were discovered by Mike Gordon in 2005. Gordon, an Aspen High School graduate, was exploring the adjacent properties owned by his mom and stepfather, Jessica and Bennett Bramson, and his grandparents when he discovered unusual bones. Gordon was a college student at Colorado State University at the time. He took bone samples to museum staff members and college educators and learned they were from a dinosaur.

The Bramsons contacted various museums about the bones in hopes of interesting them in a dig, but early suspicions were that the fossil was from a much more common dinosaur. They weren’t interested.

Foster and the Museum of Western Colorado came onto the scene about four years ago after a call from Jessica Bramson. Foster was excited to find a site in the mountains where the Morrison Formation was exposed and provided a large amount of “material.”

The Morrison got chopped up in the mountains by geologic activity, he explained, and where it is exposed at the surface is usually covered by forest. The Old Snowmass site was unusual because of the accessibility.

At first, Foster thought they were looking at a meat-eating dinosaur, which excited him because carnivores are slightly less common than plant-eaters. In one of their first digs, they pulled an 800-pound slab of rock wrapped in plaster and burlap down the hillside, removed the rock and pieced together tiny fragments of bone. It took 18 months of work to process that batch, Foster said. He compared it to working on a 3-D jigsaw puzzle.

The fossil was exposed to the Rocky Mountain Uplift, millions of years of freeze-and-thaw cycles and attacks by plant roots.

“It’s had a rough go of it,” Foster said. “It’s not the prettiest specimen.”

Their initial hauls included vertebrae, ribs and a pelvis bone.

“By 2011, I was beginning to suspect it was a haplocanthosaurus,” Foster said, citing clues he found in the bones.

It was frustrating because he wasn’t positive. Then it dawned on him that the vertebrae of many sauropods are hollow. He took his specimen to a Grand Junction hospital for a scan and found they were solid. He took his findings to a paleontologists’ convention in Los Angeles and consulted with peers to confirm his suspicions.

The haplocanthosaurus is similar to the brontosaurus, though on a much smaller scale. The brontosaurus was roughly 70 feet long and 15 feet high at the back, Foster said, while the haplocanthosaurus was 35 to 40 feet long and as tall as 8 feet at the top of the back. Both had long necks with small heads.

“Proportional-wise, it would have looked fairly similar,” Foster said.

Of the 10 known haplocanthosaurus fossils, none is close to intact. There are “three or four” partial skeletons and small amounts of bone among the remainder, Foster said.

“Nobody has yet found any skull material,” he said.

That motivates him to keep digging in Old Snowmass. Only a small fraction of the haplocanthosaurus has been found to date. The Museum of Western Colorado will continue to work at the site when possible. Foster said the museum is grateful for the access provided by the property owners. The Bramsons are equally enthused about the work continuing. Jessica and Mike Gordon, in particular, have volunteered a lot of time at the dig.

“If we find the head or teeth, it will be really earth-moving,” Bennett Bramson said.

The discovery of the 150 million-year-old haplocanthosaurus has been overshadowed by the incredible haul of bones from woolly mammoths and other prehistoric animals at Ziegler Reservoir in Snowmass Village. Foster said there is no significance to the discoveries coming only six miles apart. The mammoths are from about 10,000 years ago, while the haplocanthosaurus roamed the earth 150 million years ago.

The discovery of the haplocanthosaurus has reignited Bramson’s childhood fascination with dinosaurs.

“You go, ‘150 million years old. It was once walking this world. It was a living, breathing creature,’” Bramson marveled.

Foster said he aims to get an “official publication note” about the haplocanthosaurus find, and then parts of the fossil will likely be displayed at the museum.